3 o2 ORIGIN OF THE EARTH 



system, it would not have acquired a rate of rotation rapid enough 

 to detach matter from its equator until -it had contracted well within 

 the orbit of the innermost planet. 



7. If the nebula were a spheroid of gas whose density followed 

 the law of gases, and if it had a rotation rapid enough to shed rings 

 from its equator as the theory supposes, its moment of momentum 

 would need to have been very much greater than the system now 

 possesses. This is at variance with the established law that the 

 moment of momentum of such a system must remain constant. 

 To separate Neptune, the moment of momentum would need to 

 have been 200 times what it is; to separate Jupiter, 140 times; to 

 separate the earth, 1,800 times. These are enormous discrepancies 

 and they are not consistent with one another. 



8. Comparing the masses of the planets with the moments 

 of momenta they carried off from the parent nebula, strange dis- 

 crepancies appear. The matter in the ring supposed to have formed 

 Jupiter and his moons had a mass less than YIOOO that of the 

 nebula at the time of separation; but Jupiter and his moons have 

 about 95 per cent of the total moment of momentum which the 

 nebula then had. The Laplacian hypothesis asks us to believe that 

 an equatorial ring, having a mass less than YIOOO that of the parent 

 body, carried off 95 per cent of the total moment of momentum 

 when it separated. The supposed separation of other rings involves 

 similar incredible ratios. 



9. Under the Laplacian hypothesis, the satellites should all 

 revolve about their planets in the direction in which the planets 

 rotate on their axes; but the sixth satellite of Jupiter and the ninth 

 satellite of Saturn revolve in the opposite direction. 



10. Our knowledge of nebulae has been extended greatly in 

 recent years, but nebulae with such rings as the Laplacian hypothe- 

 sis calls for have not been found. 



The force of these objections appears to be such as to make the 

 hypothesis untenable. 



2. The meteoritic hypotheses. It was long ago noted that 

 shooting stars enter the upper atmosphere in great numbers, and 

 that occasional fragments of stony and metallic matter fall to the 

 earth. Out of this grew the notion that the earth may have been 

 built up in this way, save that the process was more rapid in the 

 early days of the earth's history. This notion, however simple 

 and natural, may be dismissed without serious consideration, for 



